Combined condensate return, boiler feed and blowdown tank

ABSTRACT

An arrangement is disclosed in which a single tank functions both as a condensate return and boiler feed tank and as a blowdown tank in conjunction with a steam boiler. The single tank is divided into separate upper and lower sections which share a common vent pipe and a common drain. The upper section of the tank functions as a condensate return and boiler feed tank by receiving the returning condensate from the steam boiler through an opening at the top thereof and by sensing the level of the water therein and adding fresh water as necessary so as to maintain an appropriate reserve of feedwater. The lower section of the tank functions as a blowdown tank by receiving water and sludge from the boiler during blowdown and mixing them with fresh water. The combined tank costs less than do separate tanks, involves reduced installation and piping costs and required less floor space.

United States Patent 11 1 Cancilla et a1.

[ Apr. 9, 19741 [73] Assignee: Ace Tank and Heater Company,

Santa Fe Springs, Calif.

22 Filed: Nov. 15, 1972 211 Appl. No.: 306,731

[52] user. 122/382, 122/396 51 int. Cl. r221, 31/54 58 Field of Search 122/382, 383 396,403

[56] References Cited UNITED STATES PATENTS 1,020,755 3/1912 3,668,838 6/1972 McNeil et a1. 122/382)( Primary Examiner-Kenneth W. Sprague Attorney, Agent, or FirmFraser and Bogucki Gamble 122/396 [57] ABSTRACT An arrangement is disclosed in which a single tank functions both as a condensate return and boiler feed tank and as a blowdown tank in conjunction with a steam boiler. The single tank is divided into separate upper and lower sections which share a common vent pipe and a common drain. The upper section of the tank functions as a condensate return and boiler feed tank by receiving the returning condensate from the steam boiler through an opening at the top thereof and by sensing the level of the water therein and adding fresh water as necessary so as to maintain an appropriate reserve of feedwater. The lower section of the tank functions as a blowdown tank by receiving water and sludge from the boiler during blowdown and mixing them with fresh water. The combined tank costs less than do separate tanks, involves reduced installation and piping costs and required less floor space.

10 Claims, 6 Drawing Figures COMBINED CONDEN SATE RETURN, BOILER FEED AND BLOWDOWN TANK BACKGROUND OF THE INVENTION 1'. Field of the Invention The present invention relates to vapor boilers such as high pressure steam boilers, and more particularlyto accessory equipment such as condensate return and boiler feed tanks and blowdown tanks used in conjunction with such boilers. I

2. History of the Prior Art y it is common practice in a steam boiler installation to usea condensate return and boiler feed tank to collect the condensing steam after it has been generated and used and to recycle the resulting water through the boiler after adding enough fresh water to maintain an optimum reserve volume of such feedwater. Useof such tanks with steam boilers is often required by local municipal code or ordinance, such as where it would be undesirable to introduce the used steam or the resulting condensate into the environment.

I Prior art condensate return and boiler feed tanks typically comprise an enclosed shell into which the returning condensate is introduced together with fresh water. Level sensing apparatus such as a float-operated control valve is employed to maintain an optimum volume of water within the tank by adding fresh water to the tank as necessary to keep the feedwater contained therein at a selected level. An overflow outlet is provided to facilitate the escape of excess water, should the feedwater rise about a maximum acceptable level. Such tank must usually be vented or otherwise equipped so as to prevent inadvertent syphoning of the contents back into the city'water supply. The feedwater within the tank flows through an outlet and into a pump which pumps the feedwater into the associated boiler.

The pressure on the upstream side of the pump is lowered due to the pumping action. As a result water entering the pump has a tendency to boil and thereby damage or destroy the pump. It is therefore desirable that the system have a net positive suction head (N.P.S.l-l.) to prevent inadvertent boiling of the water with resultant pump damage. Net positive suction head results whenever the feed tank has a gravity head greater than the pump suction head.

Prior art blowdown tanks typically comprise an enclosed shell which is vented, which has a drain outlet and which is coupled to the associated boiler via a blowdown inlet. During prolonged use of the boiler, a sludge comprising solid particles such as lime accumulates at the bottom of the boiler. Ths sludge must periodically be removed from the boiler if reasonable boiler life is to be attained. Accordingly the boiler is periodically subjected to a blowdown process in which several inches of water and the included sludge which are at the bottom of the boiler and which are under high pressure are allowed to escape into the blowdown tank. As the water exits from the bottom of the boiler it typically vaporizes due to the accompanying decrease in pressure. The solid particles within the sludge are thereby caused to exit from the boiler with considerable force. The blowdown tank which is frequently required by local ordinance or code receives the vaporizing water and included solid particles as they exit from the boiler and converts the particles and resulting steam into a relatively safe mixture of the particles and water prior to exiting from the blowdown tank.

While the condensate return and boiler feed tank and the blowdown tank often considerably enhance a given boiler installation, such tanks areexpensive to add to the installation and often greatly increase the floor space required by the installation. The expense factor is magnified not only by the fact that the individual tanks are themselves expensive but also by the fact that a substantial amount of plumbing and venting is required to couple each individual tank to the boiler. The additional floor space taken up by such tanks may become particularly critical such as in modern highrise office buildings where floor space is at a premium and therefore very expensive.

It is therefore an object of the invention to provide improved condensate return and boiler feed tanks and blowdown tanks.

A further object of the present invention is to provide a combined condensate return, boiler feed and blow down tank which utilizes hardware common to both tanks.

lt is a still further object of the invention to provide an improved blowdown tank for quickly and effectively condensing and cooling the steam and accompanying sludge during blowdown of an associated boiler.

Y BRIEF DESCRIPTION OF THE INVENTION Arrangements in accordance with the invention combine a condensate return and boiler feed tank and a blowdown tank for a vapor boiler such as a high pressure steam boiler into a single tank structure so as to reduce the cost of such tanks, the cost of their connection to the boiler and the floor space taken up by such tanks. Such a single tank in accordance with the invention is internally divided into separate upper and lower sections which respectively comprise the condensate return and boiler feed section and the blowdown section of the integral tank structure. The lower blowdown section of the tank includes a vent pipe which extends from the top end thereof through the upper or condensate return and boiler feed section to the top of the tank structure-to provide venting of the blowdown tank. An aperture in the vent pipe adjacent the top of the condensate return and boiler feed section of the tank functions both to vent the condensate return and boiler feed section and to accommodate overflow of that section in the event the liquid volume within the condensate return and boiler feed section becomes excessively large. .By integrating the structure of both tanks into a single tank the vent pipe provides a common vent used by both sections. The aperture in the vent pipe can also serve as an overflow opening and thereby provides for a common drain in which any overflow from the condensate return and boiler feed section is mixed with the contents of the blowdown section for removal from the tank via an anti-siphon drain at the bottom of the tank and within the blowdown section.

A source of fresh liquid typically comprising a direct line from the local city water supply is coupled through a float-operated level control mounted on the side of the tank adjacent the condensate return and boiler feed section to an inlet at the top of the tank. The condensate from the boiler is introduced into the condensate return and boiler feed section of the tank through a condensate return inlet at the top of the tank. The float-operated level control maintains the liquid within the condensate return and boiler feed section at a selected level by allowing fresh liquid to flow into the condensate return and boiler feed section as necessary. An outlet at the side of the tank and adjacent the bottom of the condensate return and boiler feed section facilitates the flow of liquid through a pump and into the boiler, the liquid having a net positive suction head at the pump due to the elevated location of the condensate return and boiler feed section of the tank.

During blowdown of the boiler the liquid and included sludge at the bottom of the boiler are directed into the top of the blowdown section of the tank through a blowdown inlet having a wear plate located immediately downstream thereof and curved so as to be generally tangential with the inner wall of the tank. The liquid exiting from the boiler vaporizes as it enters the blowdown section which has a pressure considerably less than that of the boiler interior. As a result the solid particles within the sludge are introduced into the blowdown section with considerable force, and the eroding action which would otherwise result is minimized by the presence of the wear plate. As the solid particles and vapor move throughout the blowdown section at high velocity they are quickly reduced to a liquid by cold liquid which is introduced into the blowdown section. The cold liquid which may also be derived from the city water supply via the same conduit or pipe that supplies the condensate return and boiler feed section of the tank is introduced into the blowdown section through an inlet in the side of the tank. The resulting mixture exits the blowdown section via the anti-siphon drain together with any overflow from the condensate return and boiler feed section.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of a combined condensate return, boiler feed and blowdown tank in accordance with the invention;

FIG. 2 is a front view of the tank of FIG. 1';

FIG. 3 is a top view of the tank of FIG. 1;

FIG. 4 is a sectional view of the tank of FIG. 2 taken along the line 4-4 thereof;

FIG. 5 is a sectional view of the tank of FIG. 2 taken along the line 5-5 thereof; and

FIG. 6 is a sectional view of the tank of FIG. 2 taken along the line 6-6 thereof.

DETAILED DESCRIPTION One preferred form of combined condensate return, boiler feed and blowdown tank 10 is shown in perspective view in FIG. 1 together with the external connections and apparatus therefor. Although the tank 10 is hereafter described in terms of its use with a steam boiler, it will be understood by those skilled in the art that combined tanks in accordance with the invention may be used with other types of vapor boilers.

The tank 10 is comprised of a generally cylindrical shell 12 mounted such that its axis of elongation is vertically disposed. A plurality of legs 14 extend downwardly from the lower end of the shell 12 to support the shell in its vertical, upright position.

As described hereafter in greater detail the interior of the shell 12 is divided into separate upper and lower sections which respectively define a condensate return and boiler feed section 16 and a blowdown section 18. The separate sections 16 and 18, although part of a single tank 10, perform the same functions as do the separate condensate return and boiler feed and blowdown tanks in the prior art, and at least in the case of the blowdown section 18 perform an additional function which improves the operation thereof.

Water comprising condensate from an associated boiler system is directed by a pipe 20 to a condensate return inlet 22 at the top of the condensate return and boiler feed section 16. Fresh water which may come directly from the local city water supply is carried by a pipe 24 to a float-operated level control 26 in the condensate return and boiler feed section 16 and through a valve 28 to a feedwater inlet 30 in the blowdown section 18. The float-operated level control 26 maintains an optimum volume of water in the condensate return and boiler feed section 16 by sensing the level of the feedwater therein and by opening so as to pass fresh water through a pipe 32 and into a feedwater inlet 34 at the top of the tank 10 as necessary. Feedwater stored in the condensate return and boiler feed section 16 exits the tank 10 at a condensate and feedwater outlet 36 where it flows through a series of valves and pipes 38 to a pump 40. The pump 40 introduces the water into the associated boiler under pressure. Since the condensate return and boiler feed section 16 comprises the upper part of the tank 10, a net positive suction head results at the upstream side of the pump 40 to greatly minimize or eliminate the possibility of the water boiling within the pump and causing cavitation which would destroy the pump.

Blowdown of the associated boiler is facilitated by opening a valve 42 to allow the water and included sludge at the bottom of the boiler to flow via a pipe 44 into the upper part of the blowdown section 18. The pressure within the blowdown section 18 is considerably less than the pressure at the bottom of the boiler. This results in the water within the pipe 44 vaporizing as it enters the blowdown section 18. However, the resulting steam and included sludge particles are quickly slowed and condensed into a mixture of water and sludge by the fresh, typically cold water introduced into the feedwater inlet 30 with the valve 28 turned on. The resulting mixture exits the blowdown section 18 via an anti-siphon drain 46 (not shown in FIG. 1). A handhole assembly 48 in the side of the tank 10 permits access to the interior of the blowdown section 18 such as for periodic cleaning.

As shown in FIGS. 2-6, the shell 12 is generally cylindrical in shape and has a generally ellipsoidal head So at the lower end thereof and a generally flat head 52 at the upper end thereof. The heads 50 and 52 respectively form the lower end of the blowdown section 18 and the upper end of the condensate return and boiler feed section 16. A second generally ellipsoidal head 54 located intermediate the heads 50 and 52 and within the shell 12 defines the upper end of the blowdown section 18 as well as the lower end of the condensate return and boiler feed section 16. The shell 12 and the various heads 50, 52 and 54 are constructed of appropriate materials such as steel and are assembled using welding or other appropriate techniques.

Combined tanks constructed in accordance with the invention comprise shells l2 and included heads 50, S2 and 54 which vary from 3/16 inch steel for boiler installations of 4-10 h.p. in size to inch steel for boiler installations of 850-1000 h.p. in size. For boiler installations of 4-10 h.p. in size the shell 12 may be approximately l8 inches in diameter with the sections 16 and 18 each being about 24 inches high. These dimensions are increased to provide greater capacity as boiler size increases. Thus a tank 10 in accordance with the invention for use with a boiler in the size range of 850-1000 h.p. has a shell 12 approximately 72 inches in diameter and sections 16 and 18 which are each approximately 60 inches high. I

A generally cylindrical vent pipe 56 is symmetrically disposed about the central vertical axis of the shell 12 so as to extend upwardly from the head 54 at its lower end through the head 52 adjacent its upper endLThe lower end of the pipe 56 opens into the blowdown section 18 while the upper end thereof is vented to the atmosphere. As shown in FIG. 6, the vent pipe 56 has an aperture 58 at one side thereof adjacent the top of the condensate return and boiler feed section 16. The aperture 58 enables the vent pipe 56 to communicate with the condensate return and boiler feed section 16. Ac-

cordingly, the vent pipe 56 forms a common ve'nt for I both the condensate return and boiler feed section 16 and the blowdown section 18 of the tank 10.

The aperture 58 also enables the vent pipe 56 to serve as part of a common drain for the sections 16 and 18. In the event the level of feedwater within the condensate return and boiler feed section 16 rises to the height of the aperture 58 the excess water flows through the aperture 58 and down the vent pipe 56 to the bottom of the blowdown section 18. The antisiphon drain 46 which forms a part of the common drainage system for the tank 10 functions to remove from the tank 10 any excess water from the condensate return and boiler feed section 16 which has flowed down the pipe 56 as well as to remove the mixture of fluid and sludge which accumulates at the bottom of the blowdown section 18 during blowdown of the associated boiler.

The float-operated level control 26 (shown only in FIG. 1) is mounted within a level control opening 60 in the side of the shell 12 within the condensate return and boiler feed section 16. The float-operated level control 26 may be of appropriate conventional construction so as to include a float (not shown) which extends into the interior of the shell 12. The float rises and drops with the level of feedwater in the condensate return and boiler feed section 16 so as to operate the level control 26 and thereby add fresh water via the feedwater inlet 34 as necessary.

During blowdown of the associated boiler, the water and included sludge are passed by the valve 42 through a short length of pipe 62 into the interior of the blowdown section 18. The pipe 62 which is mounted within a blowdown inlet 64 in the shell 12 is coupled to one end of a generally rectangular, curved wear plate 66. The wear plate 66 which is shown in detail in FIGS. 4 and 6 is curved so as to extend around the inside wall of the shell 12 from the pipe 62 at the one end thereof to an opposite end which is mounted against the inside wall of the shell 12. The wear plate 66 thus extends from the pipe 62 into contact with the inside wall of the shell in generally tangential fashion to direct the incoming flow of water and sludge in a circuitous path around the inside of the blowdown section 18. The wear plate 66 which may be fabricated of steel or other appropriate material is disposed in the path of the entering water so as to prevent erosion of the interior wall of the shell 12 which might otherwise result, particularly since the water and included sludge enter the blowdown section 18 at relatively high velocities. Due to the decreased pressure within the blowdown section 18, the entering water usually boils or vaporizes so as to further increase the problems which would otherwise be present in the absence of the wear plate 66.

In accordance with the invention the circulating mixture of steam, water and solid particles are quickly reduced in speed and condensed into a liquid-solid mixture by a supply of fresh water which enters the blowdown section 18 via the feedwater inlet 30. The resulting mixture accumulates at the bottom of the blowdown section 18 where it is removed via the anti-siphon drain 46.

It-will be seen that in accordance with the invention, the functions of the condensate return and boiler feed tank and the blowdown tank are combined into a single tank structure which requires only three heads and which places the condensate return and boiler feed section of the tank in the upper location to provide a net positive suction head. Both sections of the tank share a common vent and drain system. The practical result is a boiler installation in which the functions of several tanks as used in the prior art are combined into a single tank of greatly reduced expense and which requires considerably less floor space. The plumbing and other external connections of the integrated tank in accordance with the invention are also greatly reduced due to the close proximity of the two different sections of the tank and the fact that a significant portion of the hardware thereof is common to both tank sections.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A combined condensate return, boiler feed and blowdown tank comprising:

a generally cylindrical shell;

a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; and

means disposed within the condensate returnv and boiler feed tank and communicating with the blowdown tank to form a common vent for the combined tank.

2. The invention defined in claim 1 above, wherein the means forming a common vent for the combined tank includes means for providing an overflow for excess fluid in the condensate return and boiler feed tank.

3. A combined condensate return, boiler feed and blowdown tank comprising:

a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; and

means disposed within the condensate return and boiler feed tank and the blowdown tank for forming a common drain for the combined tank. 4. A combined condensate return, boiler feed and blowdown tank comprising:

a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; a source of fresh liquid; means coupling the source of fresh liquid to supply liquid therefrom to the condensate return and boiler feed tank; and means coupling the source of fresh liquid to introduce liquid therefrom into the blowdown tank during a blowdown process. 5. A combined condensate return, boiler feed and blowdown tank comprising:

a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; means disposed within the condensate return and boiler feed tank and communicating with the blowdown tank to form a common vent for the tank; and means disposed within the blowdown tank and associated with the common vent means to form a common drain for the tank. 6. A combined condensate return, boiler feed and blowdown tank comprising:

a integral tank structure; means dividing the interior of the integral tank structure into separate sections; means associated with one of the two separate sections for directing a returning condensate into the one section; means associated with the one section for adding liquid to the returning condensate as necessary to maintain an optimum volume of liquid in the one section; means associated with the other one of the two separate sections for receiving a blowdown mixture within said other one of the two separate sections; and means associated with the other one of the two separate sections for introducing liquid into the one of the two separate sections for mixing with the blowdown mixture. 7. A tank for use in association with a vapor boiler comprising:

a cylindrical shell mounted in an upright, generally vertical position and including first and second generally circular members respectively enclosing the top and bottom ends of the shell and a third generally circular member mounted within the shell so as to divide the interior of the shell into enclosed upper and lower sections;

means for introducing condensate from an associated boiler into the upper section of the shell;

means responsive to the level of condensate within the upper section of the shell for adding liquid to the condensate as necessary to maintain a desired level of liquid within the upper section of the shell;

means for supplying liquid within the upper section of the shell to an associated boiler; and

means for introducing into the lower section of the shell a mixture from an associated boiler during blowdown of the boiler.

8. The invention defined in claim 7 above, further including a generally cylindrical pipe vertically mounted within the shell so as to extend upwardly from the third generally circular member through the first generally circular member and form a common vent for the upper and lower sections of the shell, the pipe having an aperture therein within the upper section of the shell providing an overflow for the upper section of the shell, and means disposed within the lower section of the shell for draining from the lower section of the shell the blowdown mixture from the association boiler and overflow from the upper section of the shell.

9. The invention as defined in claim 7 above, further including means for introducing liquid into the lower section of the shell for mixing with the blowdown mixture from an associated boiler.

10. The invention defined in claim 7 above, wherein the means for introducing condensate into the upper section of the shell comprises a pipe coupled to an inlet in the first generally circular member, the means for adding liquid to the condensate includes a source of liquid, a float-operated control device mounted on the side of the shell and having a float responsive to the level of liquid within the upper section of the shell, and a pipe coupling the source of liquid through the floatoperated control device to an inlet in the first generally circular member, the means for supplying liquid to an associated boiler includes an outlet in the side of the shell adjacent the bottom of the upper section thereof, and the means for introducing a blowdown mixture into the lower section of the shell includes a pipe extending through the side of the shell adjacent the top of the lower section thereof, and a generally rectangular, curved wear plate extending between an end of the pipe within the lower section of the shell and the inner wall of the shell to define a flow path for the mixture which is generally tangential to the inner wall of the shell. 

1. A combined condensate return, boiler feed and blowdown tank comprising: a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; and means disposed within the condensate return and boiler feed tank and communicating with the blowdown tank to form a common vent for the combined tank.
 2. The invention defined in claim 1 above, wherein the means forming a common vent for the combined tank includes means for providing an overflow for excess fluid in the condensate return and boiler feed tank.
 3. A combined condensate return, boiler feed and blowdown tank comprising: a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; and means disposed within the condensate return and boiler feed tank and the blowdown tank for forming a common drain for the combined tank.
 4. A combined condensate return, boiler feed and blowdown tank comprising: a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; a source of fresh liquid; means coupling the source of fresh liquid to supply liquid therefrom to the condensate return and boiler feed tank; and means coupling the source of fresh liquid to introduce liquid therefrom into the blowdown tank during a blowdown process.
 5. A combined condensate return, boiler feed and blowdown tank comprising: a generally cylindrical shell; a condensate return and boiler feed tank disposed within and including one end of the shell; a blowdown tank disposed within and including the end of the shell opposite said one end; means disposed within the condensate return and boiler feed tank and communicating with the blowdown tank to form a common vent for the tank; and means disposed within the blowdown tank and associated with the common vent means to form a common drain for the tank.
 6. A combined condensate return, boiler feed and blowdown tank comprising: a integral tank structure; means dividing the interior of the integral tank structure into separate sections; means associated with one of the two separate sections for directing a returning condensate into the one section; means associated with the one section for adding liquid to the returning condensate as necessary to maintain an optimum volume of liquid in the one section; means associated with the other one of the two separate sections for receiving a blowdown mixture within said other one of the two separate sections; and means associated with the other one of the two separate sections for introducing liquid into the one of the two separate sections for mixing with the blowdown mixture.
 7. A tank for use in association with a vapor boiler comprising: a cylindrical shell mounted in an upright, generally vertical position and including first and second generally circular members respectively enclosing the top and bottom ends of the shell And a third generally circular member mounted within the shell so as to divide the interior of the shell into enclosed upper and lower sections; means for introducing condensate from an associated boiler into the upper section of the shell; means responsive to the level of condensate within the upper section of the shell for adding liquid to the condensate as necessary to maintain a desired level of liquid within the upper section of the shell; means for supplying liquid within the upper section of the shell to an associated boiler; and means for introducing into the lower section of the shell a mixture from an associated boiler during blowdown of the boiler.
 8. The invention defined in claim 7 above, further including a generally cylindrical pipe vertically mounted within the shell so as to extend upwardly from the third generally circular member through the first generally circular member and form a common vent for the upper and lower sections of the shell, the pipe having an aperture therein within the upper section of the shell providing an overflow for the upper section of the shell, and means disposed within the lower section of the shell for draining from the lower section of the shell the blowdown mixture from the association boiler and overflow from the upper section of the shell.
 9. The invention as defined in claim 7 above, further including means for introducing liquid into the lower section of the shell for mixing with the blowdown mixture from an associated boiler.
 10. The invention defined in claim 7 above, wherein the means for introducing condensate into the upper section of the shell comprises a pipe coupled to an inlet in the first generally circular member, the means for adding liquid to the condensate includes a source of liquid, a float-operated control device mounted on the side of the shell and having a float responsive to the level of liquid within the upper section of the shell, and a pipe coupling the source of liquid through the float-operated control device to an inlet in the first generally circular member, the means for supplying liquid to an associated boiler includes an outlet in the side of the shell adjacent the bottom of the upper section thereof, and the means for introducing a blowdown mixture into the lower section of the shell includes a pipe extending through the side of the shell adjacent the top of the lower section thereof, and a generally rectangular, curved wear plate extending between an end of the pipe within the lower section of the shell and the inner wall of the shell to define a flow path for the mixture which is generally tangential to the inner wall of the shell. 